Abstract:

A lignin-modified phenol formaldehyde resin adhesive (LPF) was prepared from the modified phenol formaldehyde resin which was treated under alkaline conditions. The performance of LPF was investigated by the dosage of lignin (L), phenol treatment time and temperature, sodium hydroxide (first batch of sodium hydroxide) and phenol/formaldehyde molar ratio (n(P)/n(F)). The results showed that LPF bond was achieved when the content of lignin was 25%, the phenol treatment time was 2 h, the treatment temperature was 80℃, the first batch of sodium hydroxide was 8%, and the phenol/formaldehyde molar ratio was 1.0:2.0. The bond strength is 1.57 MPa, which was 16.3% higher than 1.35 MPa of unmodified phenol formaldehyde adhesive (PF).0.58% of free phenol, which was 19.4% lower than 0.72% of PF.The result also showed of formaldehyde content 0.16%, solid content of 51.2%, pH value of 11.4, viscosity of 80 mPa·s, and storage period of 60 days. FT-IR analysis showed that the absorption peaks of LPF at 2893 and 1213 cm^-1 were obviously weakened, indicating that the methoxy moiety in the lignin molecule was partially shed.The absorption peak disappeared at 1505, 1320, 1114, 875 cm^-1, indicating that most of the sulfonic acid groups in the lignin disappeared during the synthesis of the phenol formaldehyde resin; the absorption peak at 1018 cm^-1 was significantly enhanced, indicating the formation of a new ether bond.

Key words: lignin, modification, phenol formaldehyde resin, adhesive